Nutrient Flux by Chinook Salmon in Idaho Streams: The Ins and Outs, and Implications for Management

Nutrient flux by Chinook salmon in Idaho streams: the ins and outs, and implications for management

Andre E. Kohler*, Timothy Copeland^§, David A. Venditti^§, Mark S. Wipfli^Ω, Bert Lewis^∞, Lytle Denny*, Josh Gable*, and Bruce Barnett^§.

Anadromous salmonids are important vectors of energy and nutrients across many landscapes.  Semelparous fishes drive nutrient fluxes across habitat boundaries and can influence community and food web structure in aquatic and terrestrial ecosystems.  The transport of marine-derived nutrients to freshwater habitats by adult Chinook salmon (Oncorhynchus tshawytscha) can fuel production across multiple trophic levels, with specific implications for freshwater productivity and the growth and survival of ESA listed fishes.  In Idaho, where 25-50% of streams are proposed to be nutrient-limited, naturally spawning spring Chinook salmon represent an important resource subsidy and linkage between marine and land-based ecosystems.  However, this flow of energy and nutrients is not uni-directional (i.e., upstream only); in addition to passive nutrient export via stream flow, smolt migrants actively export nutrients from natal freshwater rearing habitats.  And in some cases, this nutrient export by smolts can exceed import by adults, with a profound influence on organic matter and nutrient budgets in freshwater ecosystems.  We evaluated the nutrient flux to and from streams across central Idaho using Chinook salmon adult escapement and brood year parr, presmolt, and smolt migrant data from 1998 to 2008.  This information will help scientists and natural resource managers understand nutrient flux across the landscape, and potential limiting factors affecting freshwater productivity and ESA listed populations.